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What is mole? In chemical reactions, quantities of substances are considered in terms of the number of atoms, ions or molecules present. The unit devised by chemists to express the number of atoms or ions or molecules is called mole (symbol "mol"). A Mole is defined as gram atomic mass, gram molecular mass or gram formula mass of any substances (atoms, ions or molecules) which contains 6.02e+23. entities/particles. A mole is the amount of pure substances containing the same number of chemical units as there are atoms in exactly 12 grams of carbon-12 (i.e, 6.02e+23). Formerly, the connotation of  "mole" was "gram molecular weight". Current usage tends to apply the term "mole" to an amount containing Avogadro's number of whatever unit are being considered. Thus, it is possible to have a mole of atoms, ions, radicals, electrons, or quanta. This usage makes unnecessary such terms as "gram-atom", "gram-formula weig...

                                      Molecular Mass The mass of  molecule is referred as its molecular mass. Molecular mass is defined as the sum of the atomic masses of the atoms of all the elements present in a molecule shown by its molecular formula. For example, The molecular mass of H2o is (1 amu)*2+16 amu = 18 amu.                                          Formula Mass In many substances atoms are not organized into discrete molecules but are bonded to one another in a net work and are called Ionic Compounds. Such Compounds are represented by their simplest (Emprical) formulas e.g.NaCl, SiC etc. Formula mass is the sum of the atomic masses of atoms as given in the emprical formula of the substance. Sodium chloride is represented by the simplest formula NaCl which mea...

Atom is an extremely small particle. It is not possible to weigh it directly. Therefore we take its mass by comparing with slected Standard Atomic mass of C-12 (the  stable light isotope of carbon) Atomic mass is defined as the mass of one atom of the element compared with the mass of one atom of C-12. It is a number which tells how heavy or light an atom is as compared to the mass of another atom. The atomic mass of "Mg" is 24 which mean each atom of Mg is twice as heavy as Carbon atom. A Swedish chemist J. Berzelius (1779-1848) determined the atomic masses of elements. Atomic is the average of the masses of all the isotopes of an element with respect to their relative abundance. It is determined by multiplying the masses of all the isotopes which relative abundance and then add them up and finaly divide them by 100. For example:- Average Atomic Mass of Cu =63.55 a.m.u Mass spectrometer is a technique by means of which the relative abundance and atomic mass of th...

What are Significant Figures? The reliable digits in a number that are known with the certainty are called significant figures. The last digit of measured number is generally considered uncertain by ± 1. For Example :  0.0112g contains three S.F and uncertainty is ± 0.0001 mg. 11/2mg contains three S.F and uncetainty is ± 0.1mg. The uncertainty and the number of S.F do not change when measurement is expressed in sub units. For Example: 0.0112g = 11.2mg in 0.0112g uncertainty is ± 0.0001g and in 11.2 mg uncertainty is ± 0.1mg as 0.0001g = 0.1mg. Therefore uncertainty and number of S.F do not change. Number Of Significant Figures (Digits) Depends Upon : The accurancy of the measuring instrument. The size of the object to be measured. In any series of measurements, the measured numbers are obtained to a certain degree of precision. The precision of measured is indicated by the number of significant figures. Precision : Ho...

Chemistry has the task of investigating the materials of which the universe is made. It is not concerned with the forms into which they may be fashioned. For example the composition and structure of rubber is of really significance as compared to the shapes into which this has been fashioned like pipes, tyres and sheets etc. The materials are constantly undergoing chance in nature. For example, iron rusts, spirit evaporates, quickly, coal burns, animals digest their food,plants synthesize their own food materials and so on. Chemistry investigates such changes - The conditions under which they occur, the new substances that are formed as their result, and the energy that is absorbed or liverated by them. Chemistry also studies the way in which similar changes can be brought about in the laboratory and on a large scale in industries. As a result of investigation along these lines, chemistry has found how metals can be extracted from their oresm how infertile fields can be made fertile...